A photo-chromic material is a material that is initially transparent or translucent. The photo-chromic material can be temporarily transformed into being a reflective color by the application of an appropriate spectrum of electromagnetic radiation or light. That is, upon transformation, photo-chromic materials reflect background light and are not transparent or translucent for a period of time.
In contrast, phosphorescent materials, sometimes referred to as glow-in-the-dark materials, absorb electromagnetic radiation to become charged or activated. Upon removal of the electromagnetic radiation source, phosphorescent materials do not reflect, but emit a light of with an intensity that decays over a period of time. The light emitted by phosphorescent materials is typically visible in darkness or low background light conditions for a period of time.
The chemical makeup of photo-chromic materials is well known. For example, photo-chromic materials and compounds may be formed out of naphtacenequinones and derivatives thereof. It is known that various colors may be achieved by using derivatives of naphtacenequinones as is described in U.S. Pat. No. 4,036,805 by Tsujimoto et al. which is incorporated herein by reference.
While the chemical makeup of photo-chromic materials and compounds are well known, the application of photo-chromic materials and compounds to useful products has been rather limited.
One industrial use of photo-chromic materials is to store data in three dimensions in a solid state optical memory or an optical disk of a disk drive to try and increase data density within a given volume of space.
While industrial applications of photo-chromic materials are important, it is also desirable to use photo-chromic materials in other ways.